databases-week1-exercises.sql

-- 1. What are the names of countries with population greater than 8 million?
SELECT Name 
FROM country
WHERE Population > 8000000;

-- 2. What are the names of countries that have “land” in their names?
SELECT name from city where name like "%land";

-- 3. What are the names of the cities with population in between 500,000 and 1 million?
SELECT name from city where Population > 500000 and Population < 1000000;

-- 4. What's the name of all the countries on the continent ‘Europe’?
SELECT name from country where Continent = "Europe";

-- 5. What are the names of all the cities in the Netherlands?
SELECT name from city where CountryCode = 'nld';

-- 6. What is the population of Rotterdam?
SELECT Population from city where name = 'rotterdam';

-- 7. Which countries don't have a head of state? Hint: looks for NULL and '' values
SELECT * from country where HeadOfState is null;

-- 8. What's the top 10 least populated cities? Return the name and population
SELECT name, population from city limit 10;

-- 9. What countries in Africa have the local name the same as their common name?
SELECT * from country where name = LocalName and Continent = 'Africa';

-- 10. What countries have Spanish as official language? Hint: see countrylanguage table
SELECT country.name from country join countrylanguage  on country.code = countrylanguage.CountryCode where countrylanguage.`Language` = 'Spanish';

-- 11. What countries have official languages spoken between 1% and 10% of the population?
SELECT * from countrylanguage where IsOfficial = 't' and Percentage > 1 and Percentage < 10;

-- 12. What languages are spoken by over 90% of the population of a country? Return just the language names, but don't repeat entries
SELECT distinct language from countrylanguage where Percentage > 90 ;

-- 13. In which countries is 'Creole English' used? Order by descending percentage of speakers
SELECT country.name from country join countrylanguage on country.code = countrylanguage.CountryCode where countrylanguage.`Language` = 'Creole English' order by countrylanguage.Percentage desc;

-- 14. What are the 5 oldest countries (by independence date) with some form of republic government? Tip: there are multiple types of republic
SELECT name, IndepYear, GovernmentForm from country where IndepYear is not null and GovernmentForm like   '%republic%' order by IndepYear asc limit 5;

-- 15. For each country, how many people speak each language? Important: we want absolute values, not a percentage. Return the name of the country, the name of the language, and number of speakers of that language - Hint: you need both the country and countrylanguage tables - Hint: you can do calculations between columns, for example (SELECT a - b from table;)
SELECT country.name, countrylanguage.`Language`, round(country.Population*(countrylanguage.Percentage/100)) from country join countrylanguage on country.Code = countrylanguage.CountryCode ;


-- BONUS
-- 1. What is the total population of the world?
SELECT SUM(population) as TotalWorldPopulation FROM country;

-- 2. What is the average population of countries in Europe?
SELECT AVG(population) AS AverageEuropePopulation FROM country WHERE continent = 'Europe';

-- 3. How many *official* languages are spoken in Belgium (`BEL`)? Return the country code, and the number of languages as "Number of Languages"
SELECT CountryCode, COUNT(*) AS "Numbers of Languages" FROM countrylanguage WHERE CountryCode = 'BEL' AND IsOfficial = 'T' GROUP BY CountryCode;